Guava is Google Core Libraries for Java 1.5, it include extension libraries which provides many common pieces of code. Long long time ago apache starts with commons-* libraries, but unfortunately most of them lack java 5 support.

Currently Google Collection is included into Guava and on 30 Dec google released Google Collection 1.0-fianal version. This version is not 1.0 but it has frozen API. It’s nearly done, but it is used in google production projects now.

So, what’s inside ?

• Immutable Collections
• Multisets
• Multimaps
• New types
• Static utilitis

Immutable Collections

JDK currently has utility wrapper in Collections which can change our map/set/list into unmodifiable, but this is just a partial solution because internally our collection is mutable. Immutable means that we can never change the object state. So there are:

com.google.common.collect.ImmutableMap

An immutable, hash-based Map

com.google.common.collect.ImmutableSortedMap

An immutable SortedMap

com.google.common.collect.ImmutableBiMap

An immutable BiMap

com.google.common.collect.ImmutableCollection

An immutable collection.

com.google.common.collect.ImmutableMultiset

An immutable hash-based multiset

com.google.common.collect.ImmutableSet

A high-performance immutable Set

com.google.common.collect.ImmutableSortedSet

An immutable SortedSet that stores its elements in a sorted array.

All this Collections don’t allow Null values and Maps don’t allow Null keys or values.

Multisets

Multiset is a type of collection which allows duplicate elements and has unordered equality (lists have ordered equality). A multiset is also called bag. Multiset is better from list in such operation as contains(), checking if two collection are equal ignoring order and providing histograms (providing info about element count). Additionally Multiset performance depends on the number of distinct elements.

There are a lot of different implementation of Multiset interface.

com.google.common.collect.ConcurrentHashMultiset

A multiset that supports concurrent modifications

com.google.common.collect.EnumMultiset

Multiset implementation backed by an EnumMap.

com.google.common.collect.ForwardingMultiset

A multiset which forwards all its method calls to another multiset. (Decorator pattern alike)

com.google.common.collect.HashMultiset

Multiset implementation backed by a HashMap.

com.google.common.collect.ImmutableMultiset

Immputable hash-based.

com.google.common.collect.LinkedHashMultiset

A Multiset implementation with predictable iteration order.

com.google.common.collect.TreeMultiset

Multiset which maintains the ordering of its elements.

Multimaps

Similar to Multiset is Multimap iterface. It provides abstraction like a Map but keys aren’t unique or we can thing about this that unique key has a list of values, so if you have somewhere in the code type such as Map> Multimap is for you. As 1.0 version we’ve got Multimap interface implementation such as:

• Multimap

com.google.common.collect.ForwardingMultimap

A multimap which forwards all its method calls to another multimap.

• ListMultimap

  com.google.common.collect.ArrayListMultimap

  Multimap that uses an ArrayList to store the values for a given key

  com.google.common.collect.ImmutableListMultimap

  Immutable ListMultimap

  com.google.common.collect.LinkedListMultimap

  Implementation of ListMultimap that supports deterministic iteration order for both keys and values.

• SetMultimap
  com.google.common.collect.HashMultimap
  The multimap does not store duplicate key-value pairs.
  com.google.common.collect.ImmutableSetMultimap
  Immutable SetMultimap
  com.google.common.collect.LinkedHashMultimap
  Multimap that does not allow duplicate key-value entries and that returns collections whose iterators follow the ordering in which the data was added to the multimap.
• SortedSetMultimap

  com.google.common.collect.TreeMultimap

  Multimap whose keys and values are ordered by their natural ordering or by supplied comparators.

BiMap

BiMap is the map with unique values. Than it can be inverted so bimap.inverse().inverse() == bimap. There are few implementation of BiMap interface:

com.google.common.collect.EnumBiMap

BiMap backed by two EnumMap instances

com.google.common.collect.EnumHashBiMap

BiMap backed by an EnumMap instance for keys-to-values, and a HashMap instance for values-to-keys.

com.google.common.collect.HashBiMap

BiMap backed by two HashMap instances.

com.google.common.collect.ImmutableBiMap

Immutable BiMap

Static Utility Class

In this category there are a lot of class which has only static members to extend and provide function which are useful but not available today.

Collections2

Provides filter with Predicate and transform with Function methods

Functions

Function extension eg compose

Lists

Provides such methods as new* for easier List creation and two additional methods partition(create sublists of the same size) and transform which takes Function as a parameter and apply it to every list element.

Maps

Provides such methods as new* for easier Map creation, difference method, filter* methods with Predicate, fromProperties, transformValues with Function parameter.

Multimaps

Provides methods such as new*, synchronized*, unmodifiable*

ObjectArrays

Provides contact and newArray methods

Sets

Provides methods: differece, filter, intersecton, new*, union

Suppliers

Some Supplier extensions

Predicates

Predicate extension eg. and, or, not etc

Preconditions

Static methods to be called at beginning of methods to check preconditions.

Objects

Helper for Object class has great hashCode(Object …) method for generating hash code for multiple objects.

And more …

Ordering

Comparator with added methods to support common functions such as min, max etc. So instead of iterate over list to find min value, we can use min(Iterable) method.

MapMaker

ConcurrentMap builder, providing any combination of these features: soft or weak keys, soft or weak values, timed expiration, and on-demand computation of values.

Function

A transformation from one object to another. Used in transform static utility methods for Collection API extension.

Predicate

Determines a true or false value for a given input. Used in filter static utility methods.

Supplier

Class that supply object of single type. Used in new* static utility methods

Final thoughts

So…, in my opinion this library is must have in every project and there are a chance that this library will be standard JDK7 library, there are a lot of structures and static utility methods which makes our code much cleaner and simpler. Googler made great job!

References

• What is the Google Collections Library? – interview with authors Kevin Bourrillion and Jared Levy.
• Google Collections Home Page

Probably you think that I’m dead but it far from that. Rather I’ve got so many activities that I can’t manage writing about it on my blog. What’s a shame.

First at all in November I must finalize training. It was a lot of work to do, and preparing labs is very difficult task. The training was conducted in December and January, after that I’m very glad because we’ve got 5.24 note in 1-6 scale. Probably our note will be higher but on one of our training we have frustrated colleague with poor technology knowledge so he get nervous and he give us 2.5 note.

During this preparation, I was on JBoss Training. It was JBoss for Advanced J2EE Developers (JB261). It was in Amersfoort. It was one of the best training I’ve had. Maybe the reason was that was only four of us, so after this training participants and trainee is my freind, we have a lot of time to talk, to do extra exercises, it was great time. I have some thoughts about some post from this training.

Few days latter I went to Devoxx. It was quite good conference and we met there our friends so we had hard time, conference from morning to evening and than we tasted Belgium beers. Belgium beers are famous, if you like beer you should visit Belgium.

First Devoxx day I started with Brian Goetz with “From concurrent to parallel”. It was very nice but also hard topic. He talk about evolving concurrency API to support multi-core processors. The Brian’s wisdom is incredible. I’ve just get familiar with current concurrency API, but he is another step further. Next session I went to “Introduction to the SpringSource dm Server with Sam Brannen. It was nice talk but I went also to “How to hack and secure your java web application”, it was happened due to my involvement into security program in my company. Next session I’ve chosen “Envers” probably because Adam Warski is from Poland . Due to training the next session was obvious, so I went on “What’s new in Spring Framework 3.0?” Arjen with Alef was talking about new features in Spring Framework, and where was a lots of questions about schedule sources and new spring license policy. The last slot I was in several session and probably JavaFX with applet out of the browser stay in my mind. There was one quickie about “MinuteProject” by Florian Adler. MinuteProject is generator tool. It can generate DAO operation to hibernate/jpa and even iBatis, after this we have a little discussion about MDA and such projects future.

Next day was harder than a day before, but I started with “Be smart!” with Ivar Jacobson. You probably know Jacobson, if not try to get know something about him. It was one of the best session at Devoxx 2008. It will be on Parleys.com so Be smart and watch it. Next session was about JavaFX and after first impression I was a disappointed, but it just version 1.0 we’ll see what happen. Finally there was my favorite session javaposse.com with Belgium beer from Atlassian. After that I took break with my friends and we went outside to discuss sessions. Than I went on two sessions about Seem and preventing bugs. The last was about Hibernate Performance Tuning it was quite interesting. This day was quite nice quickies, one about Atlassian Connector for InteliJ and what I didn’t know that this plugin is developed in Poland.

The last day was short so I with my friends went to Brussels, when we stay for a whole weekend.

Quite long post. I finish it here, because after Devoxx Christmas was came .